If you enjoy working with microprocessors such as the Arduino or Raspberry Pi and would like to host classes for 10 or more people, the $25-50 boards become expensive quickly. A UK-based electronics developer created a design for a board called the Shrimp that can replicate any of the functions of an Arduino Uno but rolling your own Shrimp can be done for less than five dollars each.

You can buy the Shrimp board from the UK developer when in stock but if you'd prefer to DIY you'll find full instructions with a parts and supplier list at the source link below. That link also contains listings of workshops using the Shrimp microcontroller. Since it appears just like an Arduino Uno you can do any of the hundreds of projects for that board.